Aube Technologies RC840T 120 Electromechanical Relay with ...I recently upgraded my radiant floor heating from a simple 2 wire low voltage thermostat to a Nest thermostat (3 wire). I found that the Nest thermostat would not work with the Honeywell RA89A control relay that was originally installed.Problem: The Air conditioner outdoor unit will not come on ...Near the bottom of this page we have a real good Youtube Video made by Acservicetech that shows how to troubleshoot an air conditioner if the air conditioner outside unit is not turning on.